I don't understand why @ is not valid.
Look, I need this entry because we are configuring our DNS to respond to a Microsoft request.
The customer is starting to use Office365 and need to validade their domain to start using it in Office365 environment.

I had tried your instructions (entering zone name wth dot and leaving host filed empty) before starting this post without sucess.

I really need to create this record with host field with @.
This is a limitation of ISPConfig or BIND ?